Electrically conductive bonding tape with low passive intermodulation

Abstract

An electrically conductive bonding tape comprises an electrically conductive self-supporting first layer comprising electrically conductive opposing first and second major surfaces. The self-supporting first layer has an average thickness of greater than about 4 microns. An electrically conductive second layer is disposed on the first major surface of the self-supporting first layer and comprises at least 60% by weight of nickel. The second layer has an average thickness of from about 10 nanometers to about 27 nanometers and a first major surface facing away from the first major surface of the self-supporting first layer. The electrically conductive second layer further comprises a first coating disposed on the first major surface, wherein the coating comprises a chrome-based coating. The bonding tape further includes an adhesive third layer coupled to the second major surface of the self-supporting first layer opposite the second layer.

Description

PA103184W002ELECTRICALLY CONDUCTIVE BONDING TAPE WITH LOW PASSIVE INTERMODULATIONSummary

[0001] In some aspects of the present description, an electrically conductive bonding tape is provided. The electrically conductive bonding tape comprises an electrically conductive self-supporting first layer comprising electrically conductive opposing first and second major surfaces. The self-supporting first layer has an average thickness of greater than about 4 microns. An electrically conductive second layer is disposed on the first major surface of the self-supporting first layer and comprises at least 60% by weight of nickel. The second layer has an average thickness of from about 10 nanometers to about 27 nanometers and a first major surface facing away from the first major surface of the self-supporting first layer. The electrically conductive second layer further comprises a first coating disposed on the first major surface, wherein the coating comprises a chrome-based coating. The bonding tape further includes an adhesive third layer coupled to the second major surface of the self-supporting first layer opposite the second layer.Brief Description of the Drawings

[0002] FIG. 1A is a side view of an electrically conductive bonding tape, in accordance with an embodiment of the present description;

[0003] FIG. IB is a side view of an electrically conductive bonding tape, in accordance with another embodiment of the present description;

[0004] FIG. 2A is a side view of an electrically conductive bonding tape having an electrically conductive adhesive in accordance with another embodiment of the present description;

[0005] FIG. 2B is a side view of an electrically conductive bonding tape having an electrically conductive adhesive in accordance with an alternative embodiment of the present description; and

[0006] FIG. 3 is a side view of an electronic system featuring an electrically conductive bonding tape, in accordance with another embodiment of the present description.DETAILED DESCRIPTION

[0007] In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0008] Passive intermodulation (PIM) is the generation of interfering signals in an electric system which can result from nonlinearities in the mechanical components of a system. This occurs when certainstructural elements within the system (e.g., interconnections between components, corroded components, etc.) act like diodes, producing undesired interference signals, including the generation of harmonics or intermodulation. Sometimes, tapes and / or foils may be added to a system to provide grounding or EMI shielding for the components within the system, and these added layers can sometimes add interfaces between components which can contribute to the amount of PIM generated, degrading the performance of the system.

[0009] Low PIM surface interfaces on foil and fabric tapes are important for radio frequency (RF) electromagnetic noise reduction and improved signal-to-noise ratio (SNR) performance in modem day RF devices such as from cell phones. A common but expensive solution to provide a low PIM interface for grounding in RF or similar devices is to add a gold coating at the grounding or connection interface. However, gold is very expensive and adds significant cost to the system. Therefore, tapes with an improved backing (i.e., reduced PIM interference but without the excessive cost) are desired.

[0010] According to some aspects of the present description, new foil tape solutions are provided that can be applied to a high PIM conductive surface or nonconductive surface for grounding. The new tape solutions provide a grounding plane itself or grounding contacts on a high PIM conductive surface without much significant PIM increase at a lower cost versus a similar tape with a gold backing or a solution that uses an even more expensive sputtered gold interface on an end device surface.

[0011] In some aspects of the present description, an electrically conductive bonding tape includes an electrically conductive self-supporting first layer, an electrically conductive second layer coated on a first major surface of the self-supporting first layer, and an adhesive third layer coupled to a second major surface of the self-supporting first layer opposite the second layer. The structure of the adhesive bonding tape described herein further provides improved corrosion resistance, good electrical performance (e.g., as evidenced by low PIM and DC resistance) and good cosmetic performance (e.g., reduced visible discoloration) after heating and aging in a high temperature, high humidity environment.

[0012] In some embodiments, the electrically conductive self-supporting first layer may be electrically conductive in each of three mutually orthogonal directions (e.g., an x-axis, y-axis, and z-axis of the layer) and has electrically conductive opposing first and second major surfaces. In some embodiments, the first layer may be substantially equally electrically conductive in each of the three mutually orthogonal directions. In some embodiments, the electrically conductive self-supporting first layer may have an average thickness of greater than about 4 microns, or about 6 microns, or about 8 microns, or about 10 microns, or about 20 microns, or about 50 microns, or about 75 microns, or about 100 microns, or about 125 microns, or about 150 microns, or about 175 microns, or about 200 microns. In some embodiments, the first layer may be a copper foil layer.

[0013] In some embodiments, the electrically conductive second layer may include at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, or at least 99.5% byweight of nickel, and the layer may have an average thickness of about 10 nanometers (nm) to about 27 nm, preferably about 15 nm to about 27 nm and most preferably 18-27 nm. In some embodiments, the second layer may include a nickel alloy. The second layer may be continuous or mostly continuous across the surface and cover from 80-100% of the surface, preferably 95-100% of the surface and most preferably 99-100% of the surface.

[0014] In some embodiments, when the second layer includes a nickel alloy, the nickel alloy may include one or more of a nickel vanadium alloy (NiV), a nickel chromium alloy (NiCr), a nickel tin alloy (SnNi), a nickel phosphorous alloy (NiP), a nickel titanium alloy (NiTi) and a nickel niobium alloy (NiNb). In embodiments including a nickel vanadium alloy (NiV), a weight percentage of the nickel may be in a range from about 90% to about 96%, and a weight percentage of the vanadium may be in a range from about 4% to 10%. In embodiments including a nickel chromium alloy (NiCr), a weight percentage of the nickel may be in a range from about 70% to about 90%, and a weight percentage of the chromium may be in a range from about 10% to 30%. In embodiments including a nickel tin alloy (SnNi), a weight percentage of the nickel may be in a range from about 25% to about 45%, and a weight percentage of the tin may be in a range from about 55% to 75%. In embodiments including a nickel phosphorous alloy (NiP), a weight percentage of the nickel may be in a range from about 80% to about 98%, and a weight percentage of the phosphorous may be in a range from about 2% to 20%. In embodiments including a nickel titanium alloy (NiTi), a weight percentage of the nickel may be in a range from about 50% to about 70%, and a weight percentage of the titanium may be in a range from about 30% to 50%.

[0015] In some embodiments, the electrically conductive second layer may have a first major surface facing away from the first major surface of the self-supporting first layer. In accordance with embodiments of the present invention, and as described in more detail below, the first major surface of the electrically conductive second layer may be coated with a protective coating.

[0016] In some embodiments, the adhesive (third) layer comprises a non-conductive adhesive layer, such as a pressure sensitive adhesive (PSA) which can be made of rubber, silicone, or acrylic pressure sensitive adhesive (see e.g., Fig 1A), and may also comprise a double-sided tape (see e.g., Fig. IB).

[0017] In other embodiments, the adhesive (third) layer may comprise a conductive adhesive that may be electrically conductive in at least z-axis or thickness direction of the layer and may include a plurality of electrically conductive elements dispersed in a nonconductive pressure sensitive adhesive (see e.g., Fig. 2A). The conductive adhesive layer may also comprise a double-sided tape with conductive foils or fabrics backings (see e.g., Fig. 2B). In some embodiments, the conductive elements in the adhesive (third) layer may include one or more of conductive particles and conductive fibers. In some embodiments, the conductive particles may include insulative particles coated with one or more conductive coatings. In some embodiments, the conductive fibers may include insulative fibers coated with one or more conductive coatings.

[0018] According to some aspects of the present description, an electronic system may include a substrate including a nonconductive material, or one or more of stainless steel, aluminum, and titanium (or other conductive metal substrate or coating, including indium tin oxide). The electronic system also includes the bonding tape previously described and an electrically conductive resilient component (e.g., an electrically conductive spring clip) resiliently pressed against, and making physical contact with, the first major surface of the electrically conductive second layer. In some embodiments, the electrically conductive resilient component may include a gold coating or gold-coated connection point, the gold coating or connection point making physical contact with the first major surface of the electrically conductive second layer.

[0019] In some embodiments, the electrically conductive bonding tape may further include a protective coating layer disposed on at least one major surface of the second electrically conductive layer. This coating layer may comprise a very thin (e.g., having an average thickness between about 0.1 nm and several nm) coating. The protective coating may comprise a metallic chromium coating or a chromium-based coating, such as Cr2O3 or Cr(OH)3or a chromium-based coating further including another metal such as zinc. Such a thin protective coating protects the underlying second electrically conductive layer from damage by corrosion (such as galvanic corrosion and general corrosion).

[0020] In some embodiments, and as evidenced in the Experiments described below, the combination of a thin, Cr-based protective coating and Nickel layer results in good electrical performance without substantial discoloration after an aging test in a high temperature, high humidity environment.

[0021] The protective coating on a first major surface of the second electrically conductive layer may have an average thickness of about 0.1 nanometers (nm) to about 10 nm, preferably about 0.1 nm to about 7 nm and most preferably 0.5-5nm or even 2-5nm. The coating may be continuous or mostly continuous across the surface and cover from 80-100% of the surface, preferably 95-100% of the surface and most preferably 99-100% of the surface.

[0022] In some embodiments, the electrically conductive self-supporting first layer may further include a protective coating provided on a second major surface opposite the first major surface of the electrically conductive self-supporting first layer. This protective coating may comprise a very thin (e.g., having an average thickness between about 0.1 nm to several nm) coating. The protective coating may comprise a chromium-based coating (e.g., C Ch or Cr(OH)3). In some embodiments, the Cr-based coating may comprise a mixture or alloy of another metal, such as zinc. In some embodiments, the protective coating may comprise a metallic coating, such as Ni, Cr, Zn, and / or a combination thereof. In some embodiments, and as evidenced in the Experiments described below, the combination of a thin, Cr-based protective coating and Nickel layer results in good electrical performance without substantial discoloration after a heat and aging test in a high temperature, high humidity environment.

[0023] In particular, the protective coating disposed on the second major surface of the electrically conductive self-supporting layer may have an average thickness of about 0.1 nanometers (nm) to about10 nm, preferably about 0.1 nm to about 7 nm and most preferably 0.5-5 nm or even 2-5 nm. The coating may be continuous or mostly continuous across the surface and cover from 80-100% of the surface, preferably 95-100% of the surface and most preferably 99-100% of the surface.

[0024] Turning now to the figures, FIGs. lA and IB show side views of embodiments of an electrically conductive bonding tape 100 or 100’, respectively, according to the present description. In some embodiments, an electrically conductive bonding tape 100 / 100 ’ may include an electrically conductive first layer 10. In some embodiments, electrically conductive first layer 10 may be a copper foil. Electrically conductive first layer 10 has an electrically conductive first major surface 11 and an opposing electrically conductive second major surface 12.

[0025] In some embodiments, an electrically conductive second layer 20 may be coated on the first major surface 11 of the self-supporting first layer 10. The electrically conductive second layer 20 is substantially continuous on the first major surface 11. In some embodiments, second layer 20 may include at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, or at least 99.5% by weight of nickel. In some embodiments, the second layer may have an average thickness of about 10 nm to about 27 nm. In other embodiments, the second layer may have an average thickness of about 15 nm to about 27 nm (which corresponds to a loading (or deposition quantity) of about 0.13 grams per square meter (g / sqm) to about 0.22g / sqm). In other embodiments, the second layer can have an average thickness (or loading / deposition quantity) of about 13 nm to about 29 nm (or about 0.12 g / sqm to about 0.26 g / sqm). The electrically conductive second layer can have a major surface 21 facing away from the first major surface 11 of the self-supporting first layer 10. Major surface 21 may include a protective coating or passivation coating disposed thereon. The protective coating may be continuous or discontinuous. Depending on the thickness of the protective coating, at least a portion of major surface 21 may be exposed (exposing at least some of the nickel in the second layer 20).

[0026] As noted above, the protective coating may comprise a very thin (e.g., having a thickness between about 0.1 nm and several nm) coating, which corresponds to a loading (or deposition quantity) of from about 0.001 g / sqm to about 0.005 g / sqm. Different materials / chemistries will have different thicknesses for a given loading (or deposition quantity). For example, 1.0 nm corresponds to -0.007 g-atoms Cr / m2for metallic chromium. A chromate conversion coating layer (on surface 21) chemistry may be Cr(OH)3and will have a higher thickness of 5.25 nm for the same loading of -0.007 g-atoms Cr / m2. Accordingly, thicknesses disclosed herein may also be expressed as a loading (or deposition quantity).

[0027] The coating that is coated onto surface 21 may comprise a chromate conversion coating, chrome, zinc, zinc alloys and combination thereof. The protective coating may be coated onto the first major surface 21 of the second layer 20 using a conventional coating method, such as immersion, spraying, brushing, plating, sputtering, e-beam deposition. While complete coverage of major surface 21 is preferred, in other embodiments, small portions of first major surface 21 may still be exposed after the coating process due to the thin nature of the protective coating and / or due to placement of the point of contact (see e.g., Fig. 3).

[0028] In some embodiments, the electrically conductive bonding tape 100 / 100’ further includes an adhesive third layer 30, 30’ coupled to the second major surface 12 of the first layer 10, opposite the second layer 20. In some embodiments, such as shown in Figs. 1A and IB, the adhesive third layer 30, 30’ comprises a non-conductive adhesive layer. Examples of a suitable non-conductive adhesive third layer 30, 30’ include adhesive transfer tapes such as 3M electronic adhesive transfer tapes 9762MP and 3M PET double coated tapes such as 3M 9492MP respectively, (available from 3M Company).

[0029] By ‘coupled to’, it is meant that an intervening layer or coating may be disposed between surface 12 and adhesive layer 30, 30’. For example, optionally, the electrically conductive bonding tape can include an additional protective coating 25 coated onto second major surface 12 of first layer 10 and disposed between the adhesive layer 30, 30’ and second major surface 12. Coating 25 can further help protect first layer 10 from corrosion due to an interaction with the adhesive layer 30. For example, coating 25 can include a metallic coating layer, such as Ni, Cr, Zn, and / or a combination thereof. In some embodiments, coating 25 can have a thickness of from about 0.1 nm to about 0.7 nm (or a loading value of from about 0.001 g / sqm to about 0.005 g / sqm). In some embodiments, coating 25 comprises the same composition and deposition quantity as the protective coating disposed on surface 21. In other embodiments, coating 25 may have a different coating composition or deposition quantity.

[0030] Accordingly, in some embodiments, the adhesive layer 30, 30’ is bonded directly to surface 12, while in some other embodiments, adhesive layer 30, 30’ is bonded to coating 25.

[0031] In addition, as also shown in Fig. IB, electrically conductive bonding tape 100’ can include a double-sided PSA tape having a carrier film 35, comprising a suitable polymer film such as PET.

[0032] In other embodiments, such as shown in Figs. 2A and 2B, an electrically conductive bonding tape 100a, 100a’ can include a conductive adhesive layer 40, 41. In the embodiment of Figs. 2A and 2B, layers 10 and 20 can have similar compositions to those described above with respect to Fig. 1A. However, the adhesive third layer 40, 41 may comprise an electrically conductive adhesive. Such an electrically conductive adhesive third layer 40 may include a plurality of electrically conductive elements 31 dispersed in a substantially electrically insulative material 32. In some embodiments, at least some of the electrically conductive elements 31 may physically contact the second major surface 12 of the self-supporting first layer 10. In some embodiments, at least some of the electrically conductive elements 31 may be arranged such that the third layer 40, 41 is electrically conductive in at least in the z-axis (i.e., the z-axis as indicated in FIG. 2A, or the thickness direction of the third layer 40). The conductive adhesive can be made by any desired means that allows the conductive adhesive to achieve a conductive path between desired substrates. Common methods of making such a conductive adhesive may include the blending of conductive fillers (nickel, silver, metal coated particles, fibers, etc.) in a resin matrix and solvent coating them unto a release liner and drying and / or curing. Alternative methods include hot-melt coating, 100% solids coating, and curing (UV or thermal initiated cure initiated), etc.

[0033] Examples of a suitable conductive adhesive third layer 40, 41 include conductive adhesive transfer tapes such as 3M electronic conductive CPSA 9707 and 3M double coated conductive fabric tapes such as 971 IS, respectively.

[0034] FIG. 3 is a side view of one embodiment of an electronic system 200 featuring the embodiment of the electrically conductive bonding tape 100 of FIG. 1A. Alternatively, in other embodiments, the electronic system 200 of Fig. 3 can include any of electrically conductive bonding tapes 100’, 100a, and 100a’. The like-numbered elements of the electrically conductive bonding tape 100 of FIG. 1A shown in FIG. 3 have a similar functional description unless otherwise specified, and the description of these features may not be repeated in the description of FIG. 3.

[0035] In some embodiments, an electronic system 200 includes a substrate 80, the electrically conductive bonding tape 100 of FIG. 1A disposed on the substrate 80 with an adhesive layer 30 bonding to the substrate, and an electrically conductive resilient component 70 (e.g., a spring clip) resiliently pressed against, and making contact with, the first major surface 21 of second layer 20. As noted above, the first major surface 21 of layer 20 can include a protective coating disposed thereon. In some embodiments, the electrically conductive resilient component 70 may include a gold coating or point of contact 75, such that gold coating 75 makes physical contact with major surface 21 of second layer 20. In some embodiments, substrate 80 may include nonconductive substrates, or one or more of stainless steel, aluminum, and titanium.

[0036] In some embodiments, the electrically conductive resilient component 70 may be any appropriate conductive contact, including, but not limited to, a conductive foam, a spring clip, a screw, a spring, a pin, a conductive finger, a conductive fabric, and a conductive metal substrate that contacts major surface 21 of second layer 20 of electrically conductive bonding tape 100.Examples

[0037] Preparation and testing of four reference samples (Reference A, Reference B, Reference C and Reference D, described below) and six Example bonding tape constructions (Examples 1-6), comprising the compositions described herein, was completed. The Results and test methods are described below.

[0038] The DC resistance, harmonics, and passive intermodulation (PIM) interference for the Reference samples and the bonding tape Examples with a direct metal pin ground were measured and are presented in Table 1. For DC resistance, harmonics, and PIM measurements, lower numbers (more negative for PIM and harmonics) indicate improved performance over higher numbers. The DC resistance, PIM, and harmonics were measured using industry standard DC resistance meters, signal generators, spectrum analyzers, and duplexers as needed to configure for the specific DC resistance, PIM, or harmonics testing of the test printed circuit boards and samples under test.

[0039] In addition, each of the Reference samples and bonding tape Examples were subjected to a high temperature high humidity aging test to determine which constructions withstood potential heating effects (which could cause pin contact displacement due to thermal expansion) and corrosion. In this respect, the electrical testing was conducted at RT after 20 minutes dwell and after aging in an environmental chamber for 3 days (72 Hr.) at 85°C and 85% relative humidity.

[0040] The Reference Samples and Examples 1-6 will now be described in further detail.

[0041] Reference Sample A is a non-noble metal stainless steel 316L having a thickness of 1 mm. This reference sample did not include a conductive foil or other metal layer disposed on it.

[0042] Reference Sample B is a copper foil having a thickness of 10 pm. This reference sample included a second layer (disposed on its top surface) having 0.2 pm Nickel and 0.03 pm Gold on Nickel and a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0043] Reference Sample C is a copper foil having a thickness of 10 pm. This reference sample included a Ni second layer (disposed on its top surface) having a thickness of about 200 nm and a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0044] Reference Sample D is a copper foil having a thickness of 10 pm. This reference sample included a Ni second layer (disposed on its top surface) having a thickness of about 2000 nm and a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0045] Example 1 is a copper foil having a thickness of 10 pm. Example 1 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.15 g / sqm (which corresponds to a thickness of about 16.9 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to a thickness from about 0.7 to 3.7 nm) wherein the coating is a chromium-based coating. Example 1 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0046] Example 2 is a copper foil having a thickness of 10 pm. Example 2 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.2 g / sqm (which corresponds to a thickness of about 22.5 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to a thickness from about 0.7 to 3.7 nm) wherein the coating is a chromium-based coating. Example 2 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0047] Example 3 is a copper foil having a thickness of 10 pm. Example 3 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.3 g / sqm (which corresponds to a thickness of about 33.7 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to athickness from about 0.7 to 3.7 nm) wherein the coating is a chromium-based coating. Example 3 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0048] Example 4 is a copper foil having a thickness of 10 pm. Example 4 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.15 g / sqm (which corresponds to a thickness of about 16.9 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to a thickness from about 0.7 to 3.7 nm) wherein the coating is a chromium- and zinc-based coating. Example4 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0049] Example 5 is a copper foil having a thickness of 10 pm. Example 5 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.2 g / sqm (which corresponds to a thickness of about 22.5 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to a thickness from about 0.7 to 3.7 nm) wherein the coating is a chromium- and zinc-based coating. Example5 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.

[0050] Example 6 is a copper foil having a thickness of 10 pm. Example 6 includes a Ni second layer (disposed on its top surface) having a loading (or deposition quantity) of about 0.3 g / sqm (which corresponds to a thickness of about 33.7 nm). The Ni layer is top coated with a protective coating having a loading (or deposition quantity) in the range from about 0.001 to 0.005 g / sqm (which corresponds to a thickness from about 0.7 to 3.7 nm) wherein the coating is a chromium- and zinc-based coating. Example6 also includes a third layer having a 20 pm thick acrylic PSA disposed, opposite the second layer.Preparation of Adhesives:

[0051] As described above, an exemplary, commercially available acrylic -based pressure sensitive adhesive (PSA) was utilized in the experimental examples.Preparation of metal foil backing and final product:

[0052] The conductive second layer may be applied to the copper substrate in various conventional methods based on metal type applied (methods might include sputtering, plating, evaporation, chemical vapor deposition, E-Beam, etc.). For example, the Ni was plated to a certain thickness onto the copper foil. The protective coating can be applied to the Ni-plated foil via a conventional deposition process, such as plating.

[0053] The Examples 1-6 were prepared by laminating the foil backings on to the adhesive.

[0054] Table 1 shows the testing conditions that were utilized in the experiments.TABLE 1

[0055] Table 2 shows the test results of the Reference Samples A-D and the experimental Examples 1-6.TABLE 2

[0056] It can be seen, based on the Examples above, that the conductive tape design embodiments described herein allow for improved DC resistance, harmonics, and passive intermodulation (PIM) over the pin to substrate grounding test designs even after heating and aging in a humid environment. Further,the data shows that examples having thinner, Cr-coated Ni layers provide lower DC resistance (by at least a factor of 2) over examples having thicker Cr-coated Ni layers. Further, it was observed that foils having a Cr-coated Ni-based protective layer exhibited much less cosmetic change after high temperature high humidity aging than copper foils having a Ni-based protective layer (without a Cr coating). While Reference B provides good results, this is due to the expensive gold coating employed, which is impractical for typical commercial applications. Regarding visual observations, if the nickel layer is thinner, the color becomes more reddish, thereby the corrosion risk is increased. If the nickel layer is thicker, the metal pin contact resistance and harmonics after the aging are more increased. It was observed that corrosion takes place around the metal pin contact after aging. Therefore, it is advantageous to keep the nickel deposition quantity at or over 0.15 g / sqm for cosmetic purposes, but less than 0.2 g / sqm for electrical performance (resistance, harmonics, and PIM).

[0057] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1 , means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

[0058] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

[0059] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0060] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed:

1. An electrically conductive bonding tape comprising: an electrically conductive self-supporting first layer comprising electrically conductive opposing first and second major surfaces, the self-supporting first layer having an average thickness of greater than about 4 microns; an electrically conductive second layer disposed on the first major surface of the self-supporting first layer and comprising at least 60% by weight of nickel, the second layer having an average thickness of from about 10 nanometers (nm) to about 27 nm and a first major surface facing away from the first major surface of the self-supporting first layer, wherein the electrically conductive second layer further comprises a first coating disposed on the first major surface, wherein the coating comprises a chromebased coating; and an adhesive third layer coupled to the second major surface of the self-supporting first layer opposite the second layer, the adhesive third layer comprising a substantially electrically insulative material.

2. The electrically conductive bonding tape of claim 1, wherein the first layer is substantially equally electrically conductive in each of three mutually orthogonal directions.

3. The electrically conductive bonding tape of claim 1, wherein the first layer comprises a copper foil layer.

4. The electrically conductive bonding tape of claim 1, wherein the second layer comprises one of nickel and a nickel alloy.

5. The electrically conductive bonding tape of claim 1, wherein the second layer has a thickness of from about 15 nm to about 27 nm.

6. The electrically conductive bonding tape of claim 1, wherein the second layer has a thickness of from about 18 nm to about 27 nm.

7. The electrically conductive bonding tape of claim 1, wherein the coating comprises a chromebased coating having a thickness of from about 0.1 nm to about 3.7 nm.

8. The electrically conductive bonding tape of claim 1, further comprising a second coating disposed on the second major surface of the self-supporting first layer.

9. The electrically conductive bonding tape of claim 7, wherein the second coating comprises at least one of Ni, Cr, Zn, or an alloy thereof.

10. The electrically conductive bonding tape of claim 1, wherein the adhesive third layer comprises a non-conductive pressure sensitive adhesive.

11. The electrically conductive bonding tape of claim 1, wherein the adhesive third layer comprises a conductive pressure sensitive adhesive.

12. The electrically conductive bonding tape of claim 1, further comprising a carrier layer disposed on the adhesive third layer.

13. An electronic system comprising the electrically conductive bonding tape of claim 1.

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